1. Field of the Invention
This invention relates to a micromotion stage for use as a positioning mechanism in devices for fine positioning of objects, semiconductor production equipment, printing machines, scanning-tunneling microscopes and other such precision equipment, and more particularly to means for detecting and controlling the state, specifically the position and attitude, of a micromotion stage.
2. Description of the Prior Art
FIG. 5 shows the arrangement of a prior art micromotion stage and the associated control system. The main micromotion stage unit A shown at the bottom of the figure consists of a moving plate 1, a stationary plate 2 and six links 3 (only one shown) connecting the moving and stationary plates. The stroke of each of the links 3 can be extended and contracted by a stacked piezoelectric element 4. By controlling the strokes of the six links 3, it is possible to move the moving plate 1 with respect to the stationary plate 2 with six degrees of freedom including three degrees of translational freedom and three degrees of rotational freedom.
In the illustrated example, the means for detecting the strokes of the links 3 includes strain gages 16 (only one shown) bonded to the surfaces of the individual links 3. The strain signal produced by each strain gage 16 in proportion to its expansion/contraction is detected by a link stroke detection system B consisting of a bridge box 17, a strain AMP 18 and an A/D converter 19, and the result of the detection is output to a control unit 11. The control unit 11 produces a control signal and applies it to a piezoelectric element drive system C consisting of a D/A converter 12 and a drive AMP 13 for driving and controlling the stacked piezoelectric element 4.
In the example shown in FIG. 5, the strain gages 16 have to be bonded to the stacked piezoelectric elements 4 in precise alignment with their direction of expansion and contraction. In addition, the surface of the stacked piezoelectric element 4 on which the strain gage 16 is bonded has to be precision finished to a high degree of flatness to eliminate all waviness and other irregularities.
Furthermore, while the illustrated example enables detection and control of the individual link strokes of the micromotion stage unit A, it does not allow detection of the position and attitude of the moving plate 1. Thus the arrangement is technically disadvantageous in that the control system for controlling the moving plate 1 detects and controls only the link strokes, i.e., is merely a semi-closed system, and because of this is unable to control the position and attitude of the moving plate 1 with high precision.
The object of the present invention is to provide a micromotion stage that eliminates the work of bonding strain gages required for the fabrication of prior art micromotion stages and that, moreover, enables the detection of the position and attitude of a moving plate, which has been difficult to achieve by the prior art, to be connected with ease and high reliability.